Displaying an LCD (Liquid Crystal Display) is controlled by an LCD driver. An output stage of the driver has an output amplifier for an output signal. It is often suitable to use a Rail-to-Rail amplifier whose output amplitude swings fully in the power supply voltage range as the output amplifier.
U.S. Pat. No. 5,311,145 issued May 10, 1994 describes a circuit of an amplifier which performs Rail-to-Rail operation including a differential amplifier.
In addition, since high-speed operation is also required of an LCD driver, an amplifier having a high Slew Rate (SR) is needed.
An article described by T. Itakura et al. entitled, “A 402-Output TFT-LCD Driver IC With Power Control Based on the Number of Colors Selected” in the IEEE JSSC, vol.38, No3, March 2003, p.503–510, describes a circuit of an amplifier which has SR Enhancement. This SR Enhancement contains a Class-C amplifier which operates during a falling edge of an output signal.
However, the SR Enhancement has a problem of distorting a signal waveform generated at end of the falling edge. A Class-C amplifier switches off at the falling edge of an output signal, and the above problem is occurred because a driving force of an amplifier declines rapidly.
In addition, it is necessary to insert a condenser between a drain and a gate of an output transistor for phase compensation of an output amplifier. In order to obtain sufficient phase compensation, this condenser needs comparatively large capacity. However, in order to obtain a high SR, it is necessary to flow large charge and discharge current to the condenser. As a result a power consumption of the amplifier becomes large. This is a serious problem for example, in a portable apparatus for which low power consumption operation is needed.